U.K. couples living in separate homes should either stay apart or move in together under social isolation rules designed to tackle the spread of the coronavirus, according to a senior government adviser.

Sweeping restrictions announced by Prime Minister Boris Johnson on Monday to limit public movement and contain the disease have left people who are dating, but not living together, wondering if they will still be allowed to see each other.

Asked by reporters at a press conference in Downing Street on Tuesday, Jenny Harries, deputy chief medical officer for England, said partners in different households should “ideally” avoid visiting each other. Alternatively, they should “test the strength of their relationship” and move in together, she said.

U.K. couples living in separate homes should either stay apart or move in together under social isolation rules designed to tackle the spread of the coronavirus, according to a senior government adviser. Sweeping restrictions announced by Prime Minister Boris Johnson on...